The invention relates to munitions and firearms.
This invention has particular, but not exclusive, application to barrels each having a plurality of projectiles stacked axially within the barrel together with discrete selectively ignitable propellant charges for propelling the projectiles sequentially through the muzzle of the barrel and the sealing engagement between projectiles and barrel being such as to prevent rearward travel of the ignited propellant charge to trailing propellant charges. Such barrels will be referred to hereinafter as of the type described.
This invention has particular application to munitions and firearms inventions described in my earlier International Patent Applications Nos. PCT/AU94/00124 and PCT/AU96/00459 and my co-pending patent applications.
In my earlier International Patent Application No. PCT/AU96/00459 there is described a wedging action between the head part and the anvil part which effects a seal during firing. This seal ensures minimum loss of propellant past the projectile and maintains a seal between the next projectile and the barrel so that the ignited propellant does not pass the next remaining projectile and cause ignition of the propellant charge therebehind.
The head part is generally made from a softer material than the anvil portion which expands rearwardly so that during loading the head part is forced back over the anvil portion to wedge into sealing engagement with the bore.
If the angle # between the wedging parts and the bore is reduced such as to achieve a greater engagement pressure between the head part and the bore, the pressure that is transmitted to the bore upon firing by the wedging action increases. A point will be reached where the locking of the collar section against the bore of the barrel will be such that the spine and anvil part will swage through the nose of the collar section/head part, which may, as a result be spread up the barrel.
Also the added locking effect, before such a failure, may result in very high pressures within the barrel and possible barrel damage. While no jamming of rounds has been experienced to date it is considered that this possibility needs to be addressed, especially if high barrel pressures in the order of 60,000 psi plus are to be utilised. The present systems are intended to operate with a maximum internal pressure in the order of 40,000 psi chamber pressure.
Also illustrated in PCT/AU96/00459 is a reverse wedging arrangement between the spine and sealing means. However this arrangement utilises interlocking between collars on the sealing portion and recesses formed in the bore.
The bore recesses provide location of the projectile in a fixed position and assist in forming the gas seal during firing of the projectile freed from the recesses and locate the sealing portion during loading to enable the anvil portion to be forced rearwardly relative to the sealing portion to wedge each following projectile into a blocking arrangement in the barrel in front of its propellant charge. While this was previously understood to be necessary it resulted in a series of undesirable peripheral recesses in the bore.
This invention also aims to provide sealing means for effecting an operative seal between a projectile and its supporting barrel which will be efficient in terms of releasing for firing and for prevention of rearward travel of propellant ignited gases past a following projectile to be fired.
With the foregoing in view, this invention in one aspect resides broadly in a barrel assembly of the type described wherein each projectile has a body portion including a nose portion and a trailing portion which reduces in diameter rearwardly from said nose portion and a sealing band surrounding said trailing portion and having a substantially cylindrical outer face for engagement with the bore of the barrel and an inner face complementary to the trailing portion whereby the body portion may move rearwardly through the sealing portion to expand it outwardly into engagement with the barrel bore.
The trailing portion may reduces in steps from the nose portion or it may tapered to form a part-conical trailing surface. Preferably the nose portion is bullet shaped and has a major diameter just less than the barrel bore diameter and the trailing portion extends rearwardly from a return collar at the rear end of the nose portion or like reduction in body diameter.
Where the sealing band has a complementary part-conical inner face this ensures that the sealing band does not feather to a fine leading edge. It also provides sufficient radial space for positioning a sufficiently robust seal which will resist combustion pressures.
The rear end of the body portion may be terminated by a shoulder defining the rear limit of movement of the sealing band along the body portion. The shoulder may be utilised as a retainer to retain the sealing band on the body portion and if desired the shoulder may expand rearwardly at a relatively steep angle to match the correspondingly tapered rear inner surface of the sealing band so that upon firing at least the rear end of the sealing band is partially wedged into sealing contact with the bore.
The engagement of the shoulder could be arranged to be insufficient to lock the projectile through the sealing band but sufficient to deliver some resistance to forward movement, which can assist with the burn characteristics of the propellant charge. The shoulder may be a converging shape to engage with an outer end face of the projectile to reduce such resistance, as may be appropriate with certain projectiles. Alternatively the tapered trailing portion may extend to the rear end of the body portion.
Preferably the included angle # between the complementary tapered part-conical surfaces and the barrel bore is in the range of 5 degrees and 25 degrees and the medial wall thickness of the sealing band is less than one quarter the diameter of the barrel bore and more preferable less that one eighth the barrel bore diameter, particularly for high pressure applications where internal pressures may reach 90,000 psi. For low pressure applications of up to 40,000 psi, the range may be in the order of 5 degrees to 35 degrees. It is also preferred that the sealing band has a length in excess of half the length of the body portion.
For low pressure applications the sealing band may be in the form of a resilient sealing ring mounted on a stepped rearwardly reducing trailing portion such that it may expand stepwise into sealing engagement with the barrel bore and release stepwise upon firing. The steps may include intermediate ridges to prevent release of the sealing ring beyond an effective sealing position upon firing. Furthermore the outer cylindrical surface of the sealing band or ring may be provided with a groove or grooves in the form of a labyrinth seal.
The body portion and the sealing band may be formed of the same material but preferably the body portion is formed from a harder material than the sealing band.